The video-sharing website YouTube said on Wednesday it was restricting access in Libya and Egypt to a film that has sparked anti-US protests.

"This video - which is widely available on the web - is clearly within our guidelines and so will stay on YouTube," a spokesperson said in a statement.

"However, given the very difficult situation in Libya and Egypt we have temporarily restricted access in both countries. Our hearts are with the families of the people murdered in yesterday's attack in Libya," he added.

The move by Google-owned YouTube came in the wake of a deadly attack on the US consulate in the Libyan city of Benghazi that killed the US ambassador to the country and three of his colleagues.

US officials say extremists appear to have used protests over the controversial film - which mocks and insults the Prophet Mohammed - as a pretext to stage an assault involving small arms fire and rocket-propelled grenades that lasted several hours.

The attack followed an earlier protest in Cairo, the capital of Egypt, in which hardline Salafist Islamists stormed the US embassy compound.

No one was hurt but the US flag was torn down and replaced by the black banner favored by supporters of militant groups like Al-Qaeda, in a protest triggered by the emergence on the internet of the film.

The US-made amateur production was recently dubbed into Arabic and broadcast in part on some Egyptian-based television networks.